extends layout

block content
  h2 Sub Docs
  :markdown
    [Sub-documents](./api.html#types-embedded-js) are docs with schemas of their own which are elements of a parents document array:
  :js
    var childSchema = new Schema({ name: 'string' });

    var parentSchema = new Schema({
      children: [childSchema]
    })

  :markdown
    Sub-documents enjoy all the same features as normal [documents](./api.html#document-js). The only difference is that they are not saved individually, they are saved whenever their top-level parent document is saved.
  :js
    var Parent = db.model('Parent', parentSchema);
    var parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
    parent.children[0].name = 'Matthew';
    parent.save(callback);

  :markdown
    If an error occurs in a sub-documents' middleware, it is bubbled up to the `save()` callback of the parent, so error handling is a snap!

  :js
    childSchema.pre('save', function (next) {
      if ('invalid' == this.name) return next(new Error('#sadpanda'));
      next();
    });

    var parent = new Parent({ children: [{ name: 'invalid' }] });
    parent.save(function (err) {
      console.log(err.message) // #sadpanda
    })

  h3 Finding a sub-document
  :markdown
    Each document has an `_id`. DocumentArrays have a special [id](./api.html#types_documentarray_MongooseDocumentArray-id) method for looking up a document by its `_id`.
  :js
    var doc = parent.children.id(id);

  h3 Adding sub-docs
  :markdown
    MongooseArray methods such as [push](./api.html#types_array_MongooseArray-push), [unshift](./api.html#types_array_MongooseArray-unshift), [addToSet](./api.html#types_array_MongooseArray-addToSet), and others cast arguments to their proper types transparently:
  :js
    var Parent = db.model('Parent');
    var parent = new Parent;

    // create a comment
    post.children.push({ name: 'Liesl' });
    var doc = post.children[0];
    console.log(doc) // { _id: '501d86090d371bab2c0341c5', name: 'Liesl' }
    doc.isNew; // true

    post.save(function (err) {
      if (err) return handleError(err)
      console.log('Success!');
    });
  :markdown
    Sub-docs may also be created without adding them to the array by using the [create](./api.html#types_documentarray_MongooseDocumentArray-create) method of MongooseArrays.
  :js
    var newdoc = post.children.create({ name: 'Aaron' });

  h3 Removing docs
  :markdown
    Each sub-document has it's own [remove](./api.html#types_embedded_EmbeddedDocument-remove) method.
  :js
    var doc = parent.children.id(id).remove();
    parent.save(function (err) {
      if (err) return handleError(err);
      console.log('the sub-doc was removed')
    });

  h4#altsyntax Alternate declaration syntax
  :markdown
    _New in v3_ If you don't need access to the sub-document schema instance, you may also declare sub-docs by simply passing an object literal:
  :js
    var parentSchema = new Schema({
      children: [{ name: 'string' }]
    })

  h3#next Next Up
  :markdown
    Now that we've covered `Sub-documents`, let's take a look at [Models](./models.html).
